Materials having elastic properties, such as elastomers, are desirable in industry for their ability to resume an original shape after deformation or elongation. These materials are used in a wide range of industries and have many applications, such as, tires, belts, gaskets, gloves and foams. One example of an elastomer is natural rubber. Natural rubber represents a limited renewable source and thus other synthetic rubbers are manufactured to meet demands. The performance of elastomers, such as natural rubber and synthetic rubber, under mechanical stresses, such as stretching and elongation, is important to their ability to perform a desired function. Thus, the study of elastomers under mechanical stresses, and the data therefrom, provides valuable information for the selection of the materials for certain uses. For example, the viscoelastic properties of rubber materials directly relate to the bulk properties, e.g., rolling resistance, wet traction, of automobile tires and therefore understanding the viscoelasticity and the structure of rubber materials, which include various kinds of fillers, under deformation is important in developing new tire technology with desirable properties.
For instance, the ability of natural rubber to exhibit strain-induced crystallization has been the basis of studies. To measure strain-induced crystallinity, techniques such as wide angle X-ray diffraction (WAXD) and nuclear magnetic resonance (NMR) have been utilized. Diffraction based techniques suffer from the disadvantage that select amorphous peaks are not easily observed in high resolution alongside crystalline peaks over a range of elongation ratios. Obtaining high resolution in solid state NMR spectra generally requires rotating a sample at a frequency of several kHz and prior disclosures teach rubber ring samples being stretched over a post and rotated. Stretching rubber rings over a post presents drawbacks such as significant stretching errors, inaccurate data, and a limited maximum stretching ratio.
There remains a need for an apparatus that can accommodate elastomer samples for solid-state NMR testing such that the samples can be stretched at multiple elongation ratios up to the stretching limits of the material. The method described herein provides a robust process of stretching samples and obtaining data that can be used to evaluate the molecular structure and molecular motion of a sample, such as identifying the formation and amount of strain-induced crystalline material.